Metallocene olefin polymerization catalyst systems typically use an activator (also called a co-catalyst) to generate the active catalytic species. In general, there are two catalyst activator families: partially hydrolyzed aluminum alkyl complexes and non-coordinating anions (NCA's). Some of the most commonly employed activators used today are the partially hydrolyzed aluminum alkyls, more specifically, alumoxanes, such as methylalumoxane (MAO). In general, metallocene olefin polymerization systems that utilize NCA-type activators are more active than their MAO counterparts, but are also quite costly and sensitive to poisons which present a problem in catalyst synthesis, handling, storage and reactor operation. Alternatively, MAO-based systems are more robust than their NCA-type counterparts, but they suffer from the high cost of MAO production, the fact that MAO is typically used in large excess (relative to the amount of metallocene) and the limited shelf life of MAO.
In order to enhance polymer morphology, metallocene polymerization catalysts operated in industrial slurry and gas phase processes are typically immobilized on a carrier or a support, such as alumina or silica. Metallocenes are supported to enhance the morphology of the forming polymeric particles such that they achieve a shape and density that improves reactor operability and ease of handling. However, the supported versions of metallocene polymerization catalysts tend to have lower activity as compared to their homogeneous metallocene counterparts without a support. In general, metallocene and single-site catalysts are immobilized on silica supports.
Thus there is a need in the industry to find faster, cheaper and more efficient ways to activate metallocene catalyst compounds and there is also a need in the industry to find faster, cheaper and more efficient ways to support metallocene catalyst compounds.
Others have treated a calcined silica support with triethylaluminum and used it without further calcination as a support for metallocene catalyst systems.
Of possible interest is U.S. Pat. No. 6,492,293 which discloses a catalyst for polymerization which comprises a late transition metal complex, optionally an activator compound, and a support which has been impregnated with titanium or aluminum and then calcined after impregnation. Another reference of possible interest is US 2003/0228971 which describes treating silica with hydrophobicizing agents (such as hexamethyldisilazane or trimethylmethoxysilane) followed by calcining. This support is then used to support metallocene/ionic activator catalysts, dried, and then treated with metal alkyls (see Ex. 1, 2 and 4) to “prealkylate” the catalyst.
Other references of interest include those where an undehydrated (or dried and then treated with water) silica support is treated with trimethylaluminum and used without further calcination as a support for metallocene catalysts, such as U.S. Pat. Nos. 4,912,075, 4,914,253, 4,925,821, 4,935,397, 4,937,217, 4,937,301, 5,008,228, 5,086,025, 5,147,949, 5,238,892, EP0739360, U.S. Pat. No. 6,159,888, EP0170059, US20010044374-A, and EP1125952.
Other references of interest include those that disclose treatments of silica, silica-alumina, or alumina with chemicals other than organoaluminum species (e.g. fluorides, chlorides, chromium, molybdenum, tungsten, vanadium, zinc, boron, titanium, zirconium, nickel, sulfates, triflate, bentonite, etc.), followed by calcination, loading with metallocene and triethylaluminum (or other organoaluminum species), and use thereof for polymerization, including WO0144309, U.S. Pat. Nos. 6,300,271, 6,376,415, 6,391,816, 6,395,666, 6,524,987, 6,531,550, 6,548,441, 6,548,442, 6,576,583, 6,613,712, 6,613,852, 6,632,894, US20030232716, and U.S. Pat. No. 6,667,274.